This invention relates to transducer apparatus and, more particularly, to a phase-sensitive transducer apparatus of the type comprising first and second relatively movable members wherein the first relatively movable member has a plurality of windings and the second relatively movable member has a winding, and means for applying a first input signal to one of the windings of the first relatively movable member and a second input signal to another of the windings of the first relatively movable member, an output signal being induced on the winding of the second relatively movable member. In this type of transducer apparatus, the first and second input signals are generally sinusoidal in nature of substantially identical frequency and peak amplitude and are phase-displaced by a predetermined amount, and the output signal is substantially constant in peak amplitude and variable in phase during relative movement of the first and second relatively movable members.
Phase sensitive transducer apparatus of the above type have been used in systems where it is desired to sense and record and/or control movement of a movable element. This is generally accomplished by kinematically coupling the second relatively movable member, above defined, to the movable element in order that they are movable in synchronism. The first relatively movable member remains fixed and may thus be considered a stator and the second relatively movable member may be considered a rotor. The output signal from the rotor winding is phase-modulated in the sense that its peak amplitude remains constant and its phase changes during movement of the rotor and thus movable element relative to the stator. Then, by appropriately demodulating the output signal, a position signal may be derived which is periodic in nature in response to rotor movement wherein each new period of the signal is indicative of movement of the rotor and thus corresponding movement of the movable element a predetermined incremental distance.
U.S. Pat. No. 3,191,010 discloses a phase-sensitive transducer apparatus of the above-described type as used in a position measuring system. The stator has a pair of windings which respectively receive a pair of sinusoidal signals of substantially identical peak amplitude and frequency, but phase-displaced by 90.degree.. The output signal from the single rotor winding is then a sinusoidal signal having the same peak amplitude and frequency as each of the sinusoidal inputs to the stator, but a phase which varies as a function of the position of the rotor relative to the stator.
Great care must be taken to positively insure that the two sinusoidal input signals to the stator windings are substantially identical in peak amplitude, otherwise the output signal form the rotor will erroneously reflect true relative movement and position. In the transducer apparatus of U.S. Pat. No. 3,191,010, a polyphase generator is employed to convert a 4KHz square-wave input signal into a pair of 90.degree. phase displaced 1KHz sine-wave signals of the same peak amplitude and frequency. In that polyphase generator, a pair of 90.degree. phase-displaced square-wave signals are first generated and are then fed through respective bandpass filters to derive the pair of 90.degree. phase-displaced sine-wave signals. In order for these latter two signals to be identical in peak amplitude, it is clear that the bandpass filters must be perfectly or substantially perfectly matched in all respects. Also, the clock frequency must be accurately maintained at a constant value in view of the use of matched filters. As a practical matter, such perfection and accuracy is very difficult to achieve and, even if achievable, would be extremely expensive.
U.S. Pat. No. 3,876,888 discloses an apparatus capable of synthesizing a pair of phase-displaced sine-wave signals of substantially identical frequency and peak amplitude from a plurality of mutually phase-displaced square waves all of identical frequency and peak amplitude. Maintaining the amplitudes of the two sine-wave signals constant and substantially identical is much more accurate than with the type of polyphase sine-wave generator employed in the apparatus of U.S. Pat. No. 3,191,010, which utilizes bandpass filters.
It would be desirable, therefore, to provide in a phase-sensitive transducer apparatus of the general type disclosed in U.S. Pat. No. 3,191,010 a more effective and accurate multi-phase sine-wave generator so as to insure the phase-displaced sine-wave signals generated therefrom and applied to the stator windings are substantially identical in peak amplitude, thereby substantially reducing the likelihood of an erroneous phase-modulated output signal from the rotor winding.